1. Field of the Invention:
This invention relates to photosensitive elements having high sensitivity. More particularly the invention relates to an anodized aluminum or aluminum alloy plate as a support having silver halide contained in the pores of an oxide layer formed on the surface of said plate.
2. Description of the Prior Art:
Heretofore, silver salt photographic elements utilizing an anodized aluminum have been well known and are described, for example, in U.S. Pat. Nos. 2,115,339, 2,126,017 and 2,766,119.
Many reports have also been made as to the aluminum oxide layer (hereinafter referred to as alumite for convenience) formed on the surface of the aluminum by anodic oxidation, and in particular a detailed explanation as to the structure thereof is made in J. Elec. Chem. Society, 100, (9), 411.
This alumite layer is composed of hexagonal prism units (cells) standing vertically on the surface of the aluminum. A pore generally of 100 to 1,000 A in size is present in the central portion of each cell.
The predominant characteristic of such silver salt photographic elements using an anodized aluminum plate consists in durability inherent to the alumite layer due to its corrosion resistance and as a result the silver image can be protected, giving thereby semi-permanently storageable image recordings.
Therefore, it becomes necessary not only to simply place the photosensitive silver salt on the alumite layer, but to incorporate the silver salt into the pores of the alumite layer.
Silver halides, which are conventionally known photographic light-sensitive materials, are prepared, as is well known, by reacting silver nitrate with an alkali metal halide, in a gelatin solution. The resulting silver halide grains are ripened and while keeping the ripening temperature at a given temperature level by warming, the silver halide grains grow with the result thereby being that their photosensitivity is enhanced. It is known that, when the silver halide grains are prepared without the aid of any particular chemicals, their photosensitivity will depend upon the size of the silver halide grains, i.e. those grains of a smaller grain size will give relatively low photosensitivity. The grain size of silver halides used in photographic light-sensitive elements and prepared in the conventional manner will be within the range of from about 0.1 to 1.0 micron.
In contrast to this, the light-sensitive silver salts to be formed in the pores of an alumite layer are required to be of the grain size below about 1,000 A (0.1 micron). Therefore, silver salt containing photographic aluminum plates obtained by heretofore known methods are low in photosensitivity. Due to their low photosensitivity, they cannot possibly be used in making an enlargement from a small negative and, even when the image is formed using contact printing, they will require an exposure time on the order of several tens of seconds.